Pressure inversion process of making hard board products



- UNITED STATES PATENT OFFICE I 1' awe-r50 PRESSURE INVERSION PROCESS OFMAK- ING HARD BOARD PRODUCTS William H. Mason and Charles H. Westphalen,

Laurel, Mlss., assignors to Masonite Corporation, Laurel, Miss, acorporation of Delaware No Drawing. Application April 12, 1934,

' Serial him-720,247

17 Claims. (Cl. 92-61) The present invention relates, to a process ofpress such as is preferably used, provision may making hard fiberproducts, andis an improvebe made for equalizing the pressure ontheindiment on the, patent to Mason No.-1',663,505, vidual boards.granted March 20th, 1928. The invention has for The pressure initiallyapplied is extra high and 5 an object to enable the production of animproved is adapted to press out substantially the maximum hard board orother fiber product practically free quantity of expressible liquidwater, and to secure from surface defects, by providing an improvedextra high surface qualities in such skin-like mode of hot pressing,herein called a pressure portion -of the board as is being consolidatedinversion process. In accordance with the imat the smooth surfacefarthest from the wire proved pressure inversion process, extra highmesh, through which mesh the expressed wal0 pressure is initiallyapplied for a short interval ter escapes. The escaping water carrieswith it to a fiber body, or wet lap containing considersolubles; and theresulting reduction of solubles able water, as for example, more than25% ,of remaining in the board is-of advantage because, water, usuallymore'than 50% of water. 'I'herewith too great soluble content, there isincreased after the pressure is reduced and the hot prestendency toproduction of surface defects. Some 1.) sure operation is carried onunder such reduced saving in expense and reduction in drying timepressure, except that for the higher density are obtained by theefllcient expression of liquid boards the pressure may be raised againwhen water. Y the moisture content has been sufliciently re- Afterashort interval at the extra-high initial duced. pressure the wateroutflow is over, and the pres- 20 A further object is to save dryingtime and the sure, preferably without ever being completely expenseofheat-drying out of water, which by released, is reduced to a lowerpressure adapted the present process is pressed out more effectively incombination with the effect produced by the by the high initialpressure. Other objects will ig er in ia Pressure to Yield a board ofthe appear in the following description of illustrative sired density.About one minute at the extra 25 procedure, it being understood that theinvention high pressure and one-half minute time for iis not limited tothe particular procedures defooting the redu n have v n good r tsscribedherein, but is as broad as the claims. In making a board of l1.05specific gravity,

The fiber to be used is made from growths, for example, the extra highinitial pressure may such as trees, grasses, canes, corn-stalks, and thebe about 400-500 pounds per square inch, and 30 like containingligno-cellulose fiber; The ra reduced after about one minute to about100-125 materials may be shredded or ground or fibrated P d per Sq einch and drying completed in in other ways, so long as plenty of thenon-celluabout 10 minutes or less for a board thick. lose content isretained in the fiber with the Lower or higher pressures will reduce orraise cellulose to secure elfective coalescing or bonding the density.It was noted, for example, that with 35 with high wet strength of thehot pressed board. an initial p ssu of 200 p u s p r squa i Explosion byhigh pressure steam of wood chips, ed y a reduced Pressure of 60 poundsp followed by partial refining, as by beating, is the square inch, aboard of .9 specific gravity was preferred mode of fiber preparation.Made of p du e and d y Completed in about 20 n- 40 such ligno-cellulosefiber, the product, as a utes for a board thick. These figures are 40board, has high wet strength and appears to b illustrative onlyyandthere may be considerable bonded by the natural non-cellulose materialin variation on either side. the fiber. A small percentage,as 2%, ofpetro- Use of the ordinary temperatures heretofore latum or otherwaterproofness-enhancing agent available for manufacture of hard boardfrom is preferably incorporated. Extraneous binders wet lap as, forexample, temperatures in the gen- 45 and fillers are permissible, butnot essential. eral neighborhood of 350-400 F. requires times The wetlap, usually containing about 60% of about as stated above, but amaterial saving in water is introduced in a heated platen press withtime can be obtained by heating the platens and wire mesh between a facethereof, preferably the boards to an apparently critical high tem-" thelower face, and a press platen. perature over about 430 F. andpreferably about 50 To secure best and most uniform results the 450-550F., which hasbeen found to bring out press should have provision forrapid control of a new plasticity not available at temperatures heatingsteam to the platens, controls for rapidly I below about 400 F. and.thus to make the best moving the platens toward and away from one andhardest board.

another, and in the case of a multiple platen This pressure reduction,following the initial 55 application of extra high pressure, isobserved, when using a 21 platen hydraulic press, making 20 boards at atime, to be accompanied by a temporary expansion of the boards, whichexpansion may be up to about 10 or 15% of the finished thickness ofboard, and is particularly noticeable if the pressure is reduced ratherrapidly, as may be done if desired. By this expansion the remainingwater content in'the board is apparently redistributed throughout themass and largely withdrawn from the preferably smooth finish surfacefurthest away from the wire mesh, thereby minimizing likelihood ofproducing defects at such surface.

The drying is continued at the lower pressure, preferably withoutchange, the pressure being followed up as shrinkage takes place, andmaintained until the product is dry. The shrinkage and its follow-up isreadily seen in a multipleplaten press to considerably exceed theexpansion incident to the pressure reduction.

After the moisture has been reduced, for example reduced down to around5% or less, the pressure can be increased if desired, particularly withthe higher gravity board, up to the initial extra high pressure orhigher as desired, as for example 1000 pounds per square inch, to getthe benefit of high pressures in the final stages of the operation butthe lower pressure may be carried through until the board is finished.So long as scorching is avoided, the final pressure and temperatureapplication may be kept up, and applied to the board for a time after itis dry. The steam valves to the platens can be closed and the boardsremoved as soon as dry and the platens allowed to cool somewhat beforethe next pressure application, though the heating steam may be applieduninterruptedly if desired.

- We claim:

1. Process of making hard products, such as board and the like, of abody of ligno-cellulose fiber containing a sufiiciently high proportionof non-cellulose to produce, thorough bonding and containing 25% .orover of water, which comprises pressing same in a hot press with wiremesh between the fiber body and a press platen with initial applicationof relatively high pressure, and then reducing the pressure, andcontinuing the drying of the product in place between the heated platensunder pressure considerably lower than that initially applied, but not,however, below about 60 lbs. per square inch.

2. Process as in claim 1, in which the initial pressure is several timesthe lower pressure used later.

3. Process as in claim 1, in which the body of fiber contains 50% orover of water.

4. Process as in claim 1, but in which the pressure is againraised-prior to completing the board and after the moisture has beenreduced to about 5% or under.

.5. Process as in claim 1, in which the initial pressure isapproximately 400-500 pounds per square inch, applied for approximately1 minute, followed by pressure of about 100-125 pounds per square inchapplied for approximately 10 minutes, and the hardboard produced is ofspecific gravity approximately 1-1.05.

6. Process as in claim 1, in which'the initial pressure is approximately200 pounds per square inch, applied for approximately 1 minute, followedby pressure of about 60 pounds per square inch applied for approximately20 minutes, and the hardboard produced isof specific gravityapproximately .9.

7. Process of making hard products such as board and the like, of a bodyof llgno-cellulose fiber containing a suiflciently high proportion ofnon-cellulose to produce thorough bonding and containing 25% or over ofwater, which comprises pressing same in a hot press with moisture escapeconduits between the fiber body and a press platen with initialapplication of relatively high pressure, and then, without the pressurehaving ever been completely released, completing the drying of theproduct in place between the heated press platens, and under much lowerpressure.

8. Process of making a hard board or like product which comprises nearlydrying under moderate pressure of approximately 60425 pounds per squareinch after initially applying pressure several times as high to a bodyof lignocellulose containing 25% or over of water and containing plentyof the noncellulose thereof to insure thorough coalescing and bonding,and after the board is nearly dried, completing the drying under areapplication of elevated pressure.

9'. Process as in claim 8, in which temperature of 430 F. or over isapplied to the board during the application of pressure.

10. Process as in claim 8, in which temperature of 430-550 F. is appliedto the board during the application of pressure.

11. Process of making hard products, such as board and the like, of abody of ligno-cellulose fiber containing a suficiently high proportionof non-cellulose to produce thorough bonding and containing 25% or overof water, which comprises pressing same in a hot press at a temperatureof over 430 F. and preferably about 450550 F. with wire mesh between thefiber'body and a press platen with initial application of relativelyhigh pressure, and then, without the pressure having ever beencompletely released, completing the drying under much lower pressurewhereby to make a product of high dry and wet strength and substantiallyfree from surface defects in a single press-drying operation.

12. Process of making hard products, such as board and the like, of abody of ligno-cellulose fiber containing a sufi'iciently high proportionof non-cellulose to produce thorough bonding and containing 25% or overof water, which comprises pressing same in a hot press at a temperatureof over 430 F. and preferably about 450- 550 F. with wire mesh betweenthe fiber body and a press platen making initial application ofrelatively high pressure, and then materially reducing the pressurewithout, however, completely releasing the pressure and completing thedrying of the product between the heated press platens at the reducedpressure, whereby to make a hard product of high dry and wet strengthsubstantially free from surface defects in a single pressdryingoperation.

13. The process of making hard products, such as board and the like, ofa body of ligno-cellulose fiber containing a suillciently highproportion of non-cellulose to produce thorough bonding and containing25% or over of water, which comprises pressing same in a hot press withwire mesh between the fiber body and a press platen with initialapplication of relatively high pressure whereby to drive water outespecially from that part of the body of fiber adjacent said wire mesh;redistributing the remaining water content throughout the entire fiberbody by lowering the pressure without completely releasing same, and

non-cellulose to produce thorough bonding and 1 containing 25% or overof water, which comprises pressing same in a hot press at a temperatureof over 430 F. and'preferably about 450F550" I". with wire mesh betweenthe fiber body and a press platen with initial application of relativelyhigh pressure whereby to drive water out especially from that part ofthe body of fiber ad- Jacent said wire wesh; redistributing theremaining water content throughout the entire fiber body by lowering thepressure without complete- 1y releasing same, and completing thedryingwhile maintaining a pressure on said body of the lowered order ofpressure, whereby to make a hard, dense board of high dry and wetstrength and-substantially free from surface defects in a singlepress-drying operation.

15. Process of making products, such as board and the like, of a body ofligno-cellulose fiber containing a sufilciently high proportion ofnoncellulose to produce thorough bonding and con taining 25% or over ofwater, which comprises subjecting said fiber body to a single-step pressdrying operation in a hot press with wiremesh between the fiber body anda press platen com- 5 prising making initial application of relativelyhigh pressure, and then without the pressure having ever been released,completing the drying under much lower pressure, and following up suchpressure application as shrinkage occurs and until the board is dry,whereby to make a hard product of high dry and wet strength,substantially free from surface defects. l o

16. Process as in claim wherein the temperature applied in thehot-pressing is over 430' E45 and preferably about 450-550 F.

1'1. Process of making hard products such as board and the like, of abody of ligno-cellulose fiber containing a sufliciently high proportionof non-cellulose to produce thorough bonding and containing or over-o!water, which comprises pressing same in a hot press at a temperature ofabout 350-430 F. with moisture escape conduits between the fiber bodyand a press platen with initial application or relatively high pressure,and 25 then, without the pressure having ever been completely released,completing the drying of the product in place between the heated pressplatens, and under much lower pressure. I

WILLIAM H. MASON. CHARLES H.

